I have to respectfully disagree with bam70 on a few things. Firstly, these large buttons, reflections, and so on epitomize Web2.0, whether it is meant to or not. A simple Google search for Web 2.0 graphics is quite revealing.
And so on.
Secondly, the Wikipedia article agrees that AJAX is an element of Web2.0, and so are the graphics.
I am by no means saying that's what Web2.0 is, but these are most certainly elements of it. You'll also find that another component is our old friends JavaScript and DHTML. Things like dragging and dropping elements on the page, and so on. As I said above, part of Web2.0 is the buttons and graphics and so on.
However, I absolutely agree that standards compliance is a must, Web 2.0 or not. As is CSS. It will allow the majority of internet users to view your site, application, whatever it is you are working on, and doesn't preclude anybody on purpose.
I am not trying to start a fight here, and neither is bam70. But these are my experiences and opinions on web application and design.
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